This invention relates to the art of disc brakes. In particular, the invention relates to the shape and manufacture of abutment ears on a disc brake pressure plate.
Disc brakes for vehicles typically include a mounting bracket fixed to the vehicle and a brake pad movably mounted on the bracket for engaging a rotor to create frictional braking forces. The brake pad includes a friction material secured to a metal pressure plate by an adhesive, and the pressure plate is, in turn, mounted on the bracket for movement toward the rotor in response to mechanical or hydraulic forces.
The pressure plate typically has longitudinal projections, or ears, that engage lateral slots in the bracket. The ears slide in the slots toward or away from the rotor as the pressure plate moves in response to application or release of the vehicle""s brake mechanism. During application of the brake mechanism, the pressure plates are urged toward the rotor, thus creating braking forces that are transferred to the bracket by the sides of the plates and the ears.
A problem faced in this art arises because a gap must be provided between the rotor and the fixed bracket to allow the rotor to rotate freely in the absence of engagement between the rotor and the friction material. This gap is typically smaller than the combined thickness of the pressure plate and the frictional material but can be larger than the thickness of the pressure plate alone. Thus, when the thickness of the friction material has been reduced substantially, as when it is worn through use over an extended period of time, there is the possibility that the pressure plate can slide out of the slots in the fixed bracket. When this happens, the loose plate will either be thrown out of the brake assembly entirely by the rotating disc or it will become lodged between the bracket and the rotor. Either condition is clearly dangerous.
While this problem can exist in many different types of braking systems, it is more common in those systems that provide a larger tolerance for the position of the rotor, such as brake systems used with a solid rear axle drive system.
One solution to this problem has been to make the pressure plate thicker than the width of the gap, but this requires additional material, adding cost and weight. Another solution has been to bend parts of the ears of the pressure plate to make the ears thicker whereby the combined thickness of the plate and the ears is greater than the width of the gap between the rotor and the bracket. Thus, it has been proposed to bend parts of the ears in a direction away from the friction material such that the bent portions of the ears extend laterally beyond the pressure plate far enough that they remain in the slot even when the pressure plate itself is for the most part beyond the end of the slot and in the gap between the bracket and the rotor.
Significant problems are encountered when increasing the thickness of the ears by bending. One is that the bending requires application of forces to the manufacturing dies that significantly reduces the lifetimes of the dies. Another is that bending changes the shapes of the ears and moves individual parts of the ears into orientations that do not correspond with the orientations of the grooves in the fixed bracket. For example, the tips of ears after bending will lie in planes oriented differently from the planes of the grooves in the fixed housing. Thus, the tips of an ear that have been bent will lie in a plane that is not parallel to the plane containing the bent tips of the ear on the opposite side of the plate. This means that the ears that have been bent must be machined carefully both to reshape them and to make the end surfaces parallel. This requires additional, expensive operations.
Further, if an entire vertical section of the ear is bent laterally, that portion of the ear will then be displaced from the plane of the plate, resulting in application of undesirable torsional forces to the plate.
In accordance with the invention, the ears of a disc brake pressure plate are provided with sections that have been displaced laterally by the process of stamping, such as fine blanking. Thus, in accordance with the invention, the ears of a disc brake pressure plate are made laterally thicker by displacing sections of the ears only in the lateral direction. This provides several significant advantages.
For example, manufacturing the pressure plate ears by a stamping operation provides a much longer life for the forming dies because the applied forces are aligned with the direction of displacement. Further, the stamping operation is more precise than bending and keeps the end surfaces parallel. Among other advantages, this obviates the requirement to machine the ears after displacement of the sections.
The stamping operation itself employed in the invention is well known to those of skill in the art and generally involves application of a stamping die in the shape of the section to be displaced in a direction directly perpendicular to the plane of the pressure plate. Thus, a flat plate with parallel end surfaces and having the desired profile is placed in the stamping machine, and the selected sections of the ear portions are displaced linearly perpendicular to plate by application of the die. The metal of the plate flows under the force of the stamping dies to provide the desired shape to the ears.
An object of the invention is to provide a disc brake pressure plate having ears with laterally displaced sections.
Another object of the invention is to provide a unique method for making a disc brake pressure plate.
A further object of the invention is to provide a disc brake pressure plate having ears with laterally displaced sections that were formed by stamping.
A still further object of the invention is to provide a disc brake pressure plate having ears with laterally displaced sections formed by fine blanking.